Cutting oil



Patented Sept. 7, 1943 CUTTING OIL Charles E. Crawford, Cos Cob, Conn.

No Drawing. Application February 12, 1942. Serial No. 430,616

4 Claim.

This invention relates to lubricating oils and more particularly to those used for lubricating metal-cutting tools during their operation, which may otherwise be described as cutting oils. The object of the invention is .to provide such an oil having in solution a substantial quantity of elemental sulphur, that is, sulphur present chemically as such rather than in chemical combination.

The presence of sulphur or certain sulphurbearing compounds in cutting oils has long been empirically recognized as desirable. Ordinary petroleum oils, however, do not dissolve sulphur to a substantial extent. My invention is based on the discovery that by the composition or mixture of suitable oil ingredients, neither of which as such exhibits any marked capacity for dissolving sulphur, the physical solution of greatly increased quantities of sulphur to provide a highly efficient lubricating effect is made possiblewhile the other characteristics of the product are such as to render it desirable for practical use.

In order that my invention may be well understood I shall first describe a specific example thereof and thereafter discuss briefly the principles exemplified thereby.

In the preferred form of my invention which I am about to describe one of two oil ingredients,

in which when mixed or combined the sulphur is dissolved, may be an ordinary mineral oil of suitable viscosity. The other ingredient I shall refer to for convenience as distilled castor oil,

meaning thereby a product or fractional product produced from castor oil (or some similar oil as hereinafter referred to) by a suitable process and which may be further described as a liquid distillate of a boiling range below 850 F. at atmospheric pressure, of specific gravity 0.80 to 0.950, of viscosity not exceeding 200 seconds Saybolt Universal Viscosity scale at 100 F., chemically consisting of a mixture of esters and alcohols of fatty acids with or without small amounts of free fatty acids and saturated in nature. As indicated by the use of the word saturated, the iodine value is zero or substantially zero. The gum content is substantially zero.

Castor oil distillate as above referred to may be produced, for example, by the method more fully described in my copending application, Serial No. 430,617, filed Feb. 12, 1942. Briefly to describe, by way of example only, one adaptable process, the oil to be treated may be mixed with about 20% by weight of petroleum wax of about 155 F. melting point and of about 75 seconds Saybolt Universal Viscosity at 210 F. The mixture is -or indirectly, and when the temperature of the liquid of about 550 F. is reached, a reaction of thermal decomposition begins to take place with the evolution of vapor, the vapors being vented through a condenser and a vacuum pump so as to hold the process at a vacuum of about 660 millimeters (100 millimeters absolute pressure) or higher. When about 50% of the total volume of oil is distilled, the temperature of the liquid will have gradually increaseduntil a final temperature of about 650 F. has been attained. Alternatively the process may be continued until about or .of the original volume of crude oil appears in the distillate corresponding to a final temperature of about 750 F. The distillate procured by either proceeding may be utilized.

A substantial quantity of petroleum wax will be found in the distillate and may be separated therefrom in known manner by mixing there-. with petroleum naphtha of boiling range of from to 250 F. in which the wax is insoluble or nearly so, so as to decrease the solubility of the wax in the resultant mixture. A volume of petroleum naphtha equal to the volume of the oil or greater may be added for this purpose and also to give the resulting mixture a viscosity suitable for handling. The mixture is chilled by artificial refrigeration to from 0 to 20 F. and separating the wax by settling and centrifuging, the naphtha being thereafter recovered by simple distillation and condensation. The residue,

which is the distilled oil to which reference is made, may be further refined as, for example, by filtering through fullers earth or activated alumina if it is desired to do so. Other processes of production may be employed and at least one suitable distillate of castor oil is at the present time found on the market.

It is preferable to carry out the process by which the distillate is produced, as described above, within containers of stainless steel or enameled iron, since at elevated temperatures both the distillate and the residue are darkened in color by contact with iron, and this would be undesirable in some of the applications of the product.

While the distillate above referred to maybe utilized as such, it is convenient to separate it by fractionation into a lower portion boiling below 400 F. and an upper portion boiling above that temperature since the lower boiling portion is of economic value for other purposes and the upper boiling portion is equally or more satisfactory for the preparation of a cutting oil in accordance with the invention particularly due to possible loss of the lower boiling fraction by vaporization or evaporation during storage or during use.

The preferred formula for the production oi the cutting oil is the following:

i. Distillate obtained from castor oil as above referred to, V

2. Light mineral oil of viscosity 100 seconds 5. U. .V. at 100' I". or viscosity 200 seconds 8. U. v. at 100 F., 94%.

3. Sulphur, commercial grade, 1%. These component materials may be mixed in a tank or kettle and agitated. Ii' heat is added so as to bring the mixture above the first melting point of sulphur (235 F), the dissolving process is accelerated but the sulphur may be dissolved in the cold. For motives of fuel economy the entire amount of sulphur may be heated with all the castor oil distillate and about half the total mineral oil until a clear solution is obtained and the balance of the mineral oil added to the hot solution with agitation.

It is preferable to use containers of stainless steel or enameled iron for the mixing operation if heat is used, since, as stated above, the castor oil distillate darkens if heated in the presence of iron and this would detract from the clear transarent light color desirable in a cutting oil.

The final product obtained by the mixing operation is homogeneous and remains so on cooling. It is pale yellow in color, transparent and substantially free from odor, the slight odor which it has being inoffensive. In the machining of hard steels and tough alloys it gives greatly improved results over mineral cutting oil now in use with respect to finish and appearance of the work. life of the cutting tool and speed at which the cut may be taken, and it may be used to replace pure lard oil without loss of finish or efilciency and with marked saving in cost.

It is to be noted that in the light mineral oil ingredientabove referred to elemental sulphur is soluble only in such slight degree as to be of negligible effect with respect to the lubricating qualities of the pure mineral oil. Without purpcrt ing to give a scientifically accurate figure, to say that'the possible concentration is about 0.1% will indicate the approximate range and not be misleading. In the castor oil distillate itself sulphur will dissolve only to about 0.1%. But in the mixture containing about 5% of the castor oil distillate and mineral oil as above described, more than 1% of sulphur can be dissolved by a simple heating with agitation as described. Solubility falls off very rapidly if the percent of castor oil distillate is reduced below 2'/2% and no substantial increase is accomplished when the addition is beyond about 10%. Some variation in sulphur solubility will occur due to variations in the character of the castor oil itself from one batch to another within reasonable limits and likewise if some fatty oil other than castor is utilized as the source of the distillate.

It may be remarked that the solubility of sulphur in a given mixture of mineral oil and castor oil may be increased if the sulphur is heated separately to a temperature above its second melting point, i. e., to about 380 F. or higher, and then immediately added with agitation to the mixture of mineral oil and castor oil distillate, which is at a temperature above the first melting point of sulphur, 235 F. Then approximately twice as much sulphur can be dissolved as above described. However, this does not appear to be of commercial interest. at least as far as cutting oil is concerned. since increase in miphur content beyond about 1% does not seem to improve the effectiveness of the product.

It should be noted thatthe sulphur solubility varies considerably with temperature in any event and that the figures given above referred to solubility at ordinary room temperatures. In any mixture of mineral and castor oil distillate the solubility of the sulphur increase very rapidly with increasing temperature, but the figures for higher temperatures are not, of course, significant in the case of oil which is to be stored and applied to the work at ordinary temperatures. In actual commercial practice an amount of sulphur somewhat less than the total possible may be used to avoid any danger of crystallization of sulphur from the solution.

As to the mineral oil ingredient, any of the common commercial grades of petroleum light oils can be used made either from parafllnic or naphthenic crudes and varying in viscosity from 50 to 500 seconds S. U. V. The solubility of sulphur is slightly higher in the naphthenic oils than in the paraifinic, but the viscosity of the oil does not appear to have any important bearing on the sulphur solubility. Oils h gher in viscosity than 500 seconds could probably be used but no advantage would be gained as far as cutting oils is concerned. A good cutting oil can be made from a mineral oil of 100 seconds viscosity and this seems to be the most practical commercially for economic reasons.

While the product or distillate of castor oil is a preferred ingredient which I desire to claim specifically as such, in accordance with my invention in its broader aspects similar distillates of fatty oils, that is, oils of animal or vegetable origin characterized by the presence of fatty acid esters of either monatomic or triatomic alcohols or both. I may mention such semi-drying vegetable oils as corn oil, cottonseed, sesame, rapeseed and soy bean oils, drying vegetable oils such as linseed, perilla and tung oils and animal oils such as lard oil, sardine oil and menhaden oil. From these .distillates may be prepared by such a process as herein described. It will be understood that variations in the sulphur solubility figures within reasonable limits may be expected in the case of distillates from fatty oils other than castor.

While I have referred specifically to cutting oils, by suitable selection of the mineral oil ingrecient other types of lubricants may be prepared adaptable particularly for extreme pressure conditions. In such cases the mineral oil ingredient might be chosen throughout the entire lubricating range from lightest to heaviest as dictated by the nature of the final product desired. In such cases solidification by means of soap or otherwise to form a grease might be practised.

Other than the composition herein referred to, it is believed that no instance is known of a mineral oil wherein sulphur is physically dissolved in substantial quantity without including a substantial percentage of chemically combined sulphur. Oils now on the market concerning which it is claimed that they include substantial amounts of free uncombined sulphur in solution of mineral oil also include quantitative amounts of sulphur usually combined with fatty oils but sometimes combined with unsaturated components of mineral oils. Combined sulphur in mineral'oil generally has the disadvantage that it tends to form small amounts of corrosive acid in the presence of traces of moisture and then becomes in some degree corrosive to iron. Ordinarily also the odor is disagreeable. In the oil prepared as herein described the amount of combined sulphur is at best so slightas to be negligible and may be practically referred to as nonexistent.

The composition herein described may have additional agents added thereto in well known manner. I may instance scenting agents, oxidization inhibitors and wetting-out agents.

In the annexed claims I refer to a distillate of a fatty oil as meaning a product having substantially the physical and chemical descriptive properties above enumerated with respect to the product derived from castor oil. I have instanced a substantial number of crude vegetable and animal oils from which such a product may be derived, but obviously a complete catalog is impossible. In view of the complicated chemical nature of oils it will be clear that it is quite possible that certain crude fatty oils would be inapplicable but this will not mislead those skilled in the art since a simple test not of an inventive nature will disclose the fact for any given case. Moreover, certain crude products might be theoretically operative which would be of little utility practically for economic or collateral reasons.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive, as is in tact clear in several matters from the description itself. Reference is to be had to the appended claims to indicate those principles of the invention exemplifled by the particular embodiment described and which I desire to secure by Letters Patent.

I claim:

1. A lubricating oil comprising a mineral oil base of suitable viscosity with which is mixed from several percent up to about ten percent of a light saturated distillate of a fatty oil and containing dissolved therein elemental sulphur in amount from about one-half .percent to the limit of solubility and substantially excluding combined sulphur,

2. A lubricating oil comprising a mineral oil base of suitable viscosity with which is mixed from several percent up to about ten percent of a light saturated distillate of castor oil and containing dissolved therein elemental sulphur in amount from about one-half percent to the limit of solubility and substantially excluding combined sulphur,

3. A cutting oil containing at normal atmosphere temperatures from about one-fifth to two percent element sulphur dissolved in a mixture containing a distillate of a fatty oil in amount several times the weight of the sulphur and the balance of light mineral oil.

4. A cutting oil containing at normal atmospheric temperatures elemental sulphur in amount, from about one per cent by weight to the limit of solubility dissolved in a mixture of about five percent castor oil distillate and a light mineral oil.

CHARLES E. CRAWFORD. 

